Zoo Credits Gains in Birth of Rare Species to Animal Experiments

Nyrie the Cheetah bore two cubs earlier this year at the San Diego Zoo after five years of being barren. The zoo’s green iguanas have recently bred in numbers far beyond their traditional output in captivity. Scientists hope soon to stimulate reproduction in their one Komodo dragon, a species historically with almost no offspring born in zoos.

In all cases, success in boosting reproduction of these highly endangered species has resulted from implantation of hormone pumps in the animals. Scientists borrowed a technique used to help infertile women, in which an implanted device releases measured amounts of hormone to encourage ovulation.

A key factor allowing adaptation to animals was testing of the pump first in research dogs to prove that it would be safe and effective in rare, endangered animals.

The San Diego Zoo’s research chief cites his center’s work with hormone pumps as a major justification for laboratory animal research, which continues to come under attack from animal rights activists who claim such experimentation is largely unnecessary and ethically questionable, especially for zoos.

Over the years, research institutions such as medical schools and zoos have borne the brunt of such criticism. Last month, the zoo received a letter questioning its surgical use of dogs to test the hormone pump.

“The research we do is for the welfare of animals, to alleviate pain, suffering and disease in them,” said Werner P. Heuschele, director of the zoo’s Center for the Reproduction of Endangered Species, which attempts to apply precepts of modern medicine to endangered animals.

“To save the lives of zoo animals, you have to learn from (experimentation) on laboratory animals,” Heuschele said. The development of vaccines, better nutrition, and safer and more prolific reproduction among endangered species requires such work, he said, either on laboratory species such as dogs or cats, or on exotic animals themselves.

“All (of this) leads to our ultimate goal of establishing self-sustaining populations of endangered animals in captivity so we don’t take more of them out of nature. And also we hope to reintroduce some of the (zoo-born animals) back into nature.”

Heuschele has been in the forefront of scientists who have vehemently defended the need for laboratory animal research and, at the same time, pressed for stricter controls over how the animals are treated to minimize suffering and unnecessary experimentation.

The San Diego Zoological Society, under which Heuschele’s center operates, adopted a policy this year on the use of animals for research. It emphasizes the zoo’s sensitivity toward humane care and treatment, and goes beyond federal and state regulations.

The policy rules out any scientific investigations that subject animals to deliberately induced pain or traumatic injury. Nor will the zoo support such investigations by other facilities. The policy limits research to the goal of expanding the numbers of endangered animals. All proposals undergo a four-step review by zoo committees and the society’s executive director.

“I instigated this because I wanted a positive policy on animal research to tell people where we are coming from,” Heuschele said. “We strive to conscientiously maintain the best standards for animal treatment. I personally and professionally believe we should punish those who act irresponsibly in not considering pain and injury to animals in their work.

“When we do invasive procedures--use of needles or surgery, for example--we make sure to use both a pain killer and (drug to cause) lack of consciousness. Even restraint can be a discomfort, so we will use a tranquilizer to avoid any anxiety or stress or fear.

“Stressing them is counterproductive to health, which is what we are trying to maintain.”

But Heuschele just as strongly argues the case for using animals in research to improve care for animals and humans.

“When I was first trained as a veterinarian, I had to be taught using animals,” Heuschele said. “When a vet saves a dog that has been hit by a car, he uses knowledge from having practiced prosthetic on practice dogs.”

Experiments at the zoo’s research center are ongoing in several areas, including:

- Endocrinology, involving the study of hormone levels, breeding cycles, gestation and birthing. Several years ago, zoo scientists devised a test for measuring hormone levels in animals through use of waste matter samples, eliminating the need to take periodic blood samples through needles.

“There is simply no way to model certain biological mechanisms with computers” as suggested by opponents of animal research, Heuschele said, even though use of computers has increased where possible.

- Infectious diseases, including development of vaccines to prevent serious outbreaks of illness that can decimate both zoo and wild animal populations. The zoo lost its population of Pere David deer--a species extinct in nature--to malignant catarrhal fever in 1980 after keepers discovered too late that the white-tailed gnu was a carrier of the deadly virus.

“Sometimes you have to infect an animal because we are not able to study the disease in the wild,” Heuschele said. “We strive wherever possible to study the virus in the lab, growing them in human cell tissues we have in the freezer, without having to use tissue from the animal itself.”

But even if the virus can be grown without sacrificing an animal for necessary tissue, a candidate vaccine must be tested on a few animals to make sure it is safe for wide-scale use. “The ultimate test must be with the actual animal,” Heuschele said, “just as vaccines for controlling distemper in dogs or pneumonia in cattle were tested on a few dogs and cattle when first developed.”

The zoo’s primate species, often used to test vaccines before human testing takes place, now benefit from earlier biomedical research for humans and receive vaccinations for polio, measles, tetanus and rubella.

- Reproductive physiology, including semen quality evaluation, embryo transfer and artificial insemination.

The use of hormone pumps to stimulate ovulation grew out of a joint research program between the zoo, UC San Diego and Cornell University, and was partly paid for by the National Institutes of Health in Washington.

Heuschele said the safety and value of the pumps in animals had to be tested in dogs before exotic animals could be risked.

“A dog is a good model before going to much more difficult-to-handle animals,” he said. “And in this case, the dogs did not have to be sacrificed (with euthanasia). We showed that the procedure could work, and the subsequent success with the cheetah is a great accomplishment.”

Heuschele believes that animal welfare groups and animal researchers--particularly those working in zoos--can reach common ground on the issue of experimentation.

“There is a sensitivity on the part of zoo biologists toward their sacred stewardship of animals,” he said.